The officers had been charged with assault and falsifying records. Prosecutors said they were involved in a series of unprovoked attacks that left two inmates hospitalized, and all six officers were suspended after they were arrested in December 2010.

But county authorities say separate grand juries eventually declined to hand up indictments in two of the cases. And charges in the third were dismissed before a grand jury heard evidence.

Four of the officers have returned to active duty since being cleared, while two remain suspended without pay. But all six may still face internal disciplinary action.